[.pdMat {nlme} | R Documentation

## Subscript a pdMat Object

### Description

This method function extracts sub-matrices from the positive-definite matrix represented by `x`.

### Usage

    x[i, j, drop]
    x[i, j] <- value

### Arguments

`x` | an object inheriting from class `pdMat` representing a positive-definite matrix.
`i, j` | optional subscripts applying respectively to the rows and columns of the positive-definite matrix represented by `object`. When `i` (`j`) is omitted, all rows (columns) are extracted.
`drop` | a logical value. If `TRUE`, single rows or columns are converted to vectors. If `FALSE` the returned value retains its matrix representation.
`value` | a vector, or matrix, with the replacement values for the relevant piece of the matrix represented by `x`.

### Value

if `i` and `j` are identical, the returned value will be `pdMat` object with the same class as `x`. Otherwise, the returned value will be a matrix. In the case a single row (or column) is selected, the returned value may be converted to a vector, according to the rules above.

### Author(s)

Jose Pinheiro Jose.Pinheiro@pharma.novartis.com and Douglas Bates bates@stat.wisc.edu

### See Also

`[`, `pdMat`

### Examples

    pd1 <- pdSymm(diag(3))
    pd1[1, , drop = FALSE]
    pd1[1:2, 1:2] <- 3 * diag(2)

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